Each year several thousand children are born with congenital heart defects, such as pulmonary artery branch stenosis, coarctation of the aorta, and bilateral renal stenosis. Pulmonary artery branch stenosis results from underdevelopment of the pulmonary arteries, and causes a narrowing of the arteries that reduces blood flow to the lungs. It may also occur as a consequence of a previous palliative surgical procedure. Coarctation of the aorta likewise results from underdevelopment of portions of the aorta, and causes constrictions in the aorta that reduce blood flow to the extremities and adversely impact heart function. Similarly, bilateral renal stenosis, caused by underdevelopment of the renal arteries, can lead to reduced kidney function and hypertension.
An aspect common to all of the foregoing congenital diseases, as well as other pediatric constrictive diseases, is that the arteries subject to the disease grow rapidly during the early years of a child's life. For example, the pulmonary artery in an infant may double in size within the first twelve months, and continues to increase in diameter throughout the first decades of the child's life.
Previously known endoprostheses, such as those described in U.S. Pat. No. 4,733,665 to Palmaz, and U.S. Pat. No. 4,655,771 to Wallsten, are capable of only a limited range of expansion. Once such endoprostheses are deployed, they do not possess the capability to freely expand with the vessel diameter as the child grows. In particular, due to the fixed diameter of such endoprostheses, somatic growth causes the vessel to become relatively stenotic. For example, the stent described in the patent to Palmaz is incapable of self-expanding, while the stent described in the patent to Wallsten is capable of only a limited degree of radial expansion, once deployed.
While other previously known endoprostheses have been proposed, none appear suitable for use in treating congenital constrictive disease in pediatric patients. Coiled sheet stents, such as described in U.S. Pat. No. 5,306,294 Winston et al., do not possess the necessary flexibility to permit deployment through tortuous anatomy. Some stents, such as described in U.S. Pat. No. 5,441,515 to Khosravi et al. and U.S. Pat. No. 5,643,314 to Carpenter et al., provide for positive locking of the stent at a selected diameter, thereby inhibiting future expansion as the vessel grows.
Other stents, such as coil spring stents, e.g., as described in U.S. Pat. No. 4,665,918 to Garza et al., do not appear to possess the necessary resiliency to undergo the diameter changes. Instead, the coil-spring structure described in that patent-and present in most other coil-spring type stents--tends to promote tissue growth through the gaps of the coil. Consequently, such devices tend to become ingrown in the vessel wall, and may act as a permanent constriction in the vessel, rather than expanding as the vessel diameter increases. The drawback of tissue ingrowth is similarly expected to pose a problem with other stent designs. For example, the locking lugs of the stent described in U.S. Pat. No. 5,192,307 to Wall are likewise expected to engage the vessel wall and become ingrown, thereby inhibiting further expansion of the stent.
In view of the foregoing, it would be desirable to provide a prosthesis, and methods of use, suitable for use in treating congenital defects and constrictive disease wherein the device is capable of expanding to self-adjust to the growth of the vessel.
It further would be desirable to provide a prosthesis, suitable for treating congenital defects and constrictive disease, that retains its ability to support a vessel wall as the vessel diameter expands, with reduced risk of migration.
It still further would be desirable to provide a prosthesis capable of self-adjusting to a growing vessel which is designed to reduce tissue ingrowth that could restrict the capability of the prosthesis to expand in diameter as the vessel grows.
It also would be desirable to provide apparatus and methods suited for percutaneous delivery of a prosthesis capable of self-adjusting to accommodate a growing vessel.